Process for preventing or reducing after-cooking darkening in potatos

ABSTRACT

The invention relates to a process for preventing or reducing after-cooking darkening in par-fried potato food products, comprising forming treated potato food products by contacting blanched potato food products with a composition comprising lactic acid. The composition may further contain calcium lactate and/or SAPP.

This invention relates to a process for preventing or reducingafter-cooking darkening in par-fried potato food products.

After potatoes are cooked, they develop a dark bluish-gray pigmentationknown as after-cooking darkening. This pigmentation is due to formationof a complex of ferric (Fe³⁺) ions with chlorogenic acid. In freshlycooked potatoes, a colorless chlorogenic acid-ferrous iron (Fe²⁺)complex is formed, and is subsequently oxidized in air to the coloredchlorogenic acid-ferric iron complex.

Various factors are known to affect after-cooking darkening. An overviewhas been given in U.S. Pat. No. 5,391,384, which patent advocates theuse of calcium acetate. It is believed that calcium acetate and theother mentioned chemicals reduce pigmentation by sequestering orchelating the iron in the potato so that it is held in a non-ionizableform and cannot take part in a reaction with chlorogenic acid, therebypreventing the formation of the dark colored pigment.

However, despite these investigations most used chemical in preventingafter-cooking darkening in the process of making par-fried potatoproducts, such as French fries which can be made in French fryprocessors, do use SAPP (disodium acid pyrophosphate) which is now usedroutinely for the treatment of blanched potato products before fryingand freezing. SAPP treated potatoes can develop a bitter chemical taste,and more recently it has been reported to be a concern to chemicaladditive-conscious consumers. In addition, SAPP is disadvantageous inview of its cost.

There is a need to provide an improved process of achieving preventionof after-cooking darkening of potato food products.

Several patents disclose the use of calcium for pretreating potatoes.U.S. Pat. No. 2,893,878 discloses treatment of potatoes with calciumchloride to inhibit browning of raw potatoes; U.S. Pat. No. 2,894,843discloses the treatment of freshly peeled potatoes with calcium sulfiteto inhibit discoloration of the raw vegetable; U.S. Pat. No. 2,987,401discloses treatment of peeled potatoes with calcium phytate to inhibitdiscoloration of the raw potato; U.S. Pat. No. 3,051,578 discloses thetreatment of potatoes with EDTA and salts thereof, including calcium,for preventing greening in unpeeled potatoes; U.S. Pat. No. 3,063,849discloses the production of dehydrated cooked potatoes by precookingpotato slabs in water containing calcium ions; U.S. Pat. Nos. 4,818,549and 4,911,940 disclose treating apple cubes with a solution containingcalcium chloride. In addition, U.S. Pat. No. 2,212,461 discloses thepreparation of French fried potatoes in which the potato food productsare soaked for a prolonged period prior to cooking in a solution ofacetic acid to avoid a non-uniform color and burnt taste arising fromhigh sugar levels. In U.S. Pat. No. 5,391,384 the procedure of dippingblanched potato food products in calcium acetate solution in order tocontrol after-cooking darkening of French fries is disclosed. However,the use of calcium acetate in combination with the commonly used SAPPleads to precipitation of solid materials.

US 2004/022900 relates to a batter coating and to the preparation ofpotato pieces, such as French fries The process makes use of blanchingpotato pieces that may be dipped into a food preparation solutioncontaining one or more of sodium acid pyrophosphate, dextrose, salt, orcolor, after which the pieces are coated with the batter, which containscalcium lactate. The calcium lactate is added to the batter to controlor improve color. Lactic acid is not used.

In the production of potato derived products such as starches, potatoflakes, potato granules and the like often antioxidants such as sulfitesare used to prevent darkening of the products. Sulfites are allergenicand suspected to be harmful to the human body.

The present invention is directed towards a novel process for reducingor preventing after-cooking darkening in par-fried potato food products,without having the disadvantages of prior art methods, having a betterperformance without the occurrence of precipitation, and preferablyhaving additional advantages which have become important the last yearsin food processing.

According to an aspect of the invention, there is provided a process forpreventing or reducing after-cooking darkening in par-fried potato foodproducts, comprising forming treated potato food products by contactingblanched potato food products with a composition comprising lactic acid.

In a preferred aspect of the invention the lactic acid is present in atleast 0.3 wt. %, preferably at least 0.6 wt % of the composition. It wasfound that lactic acid is able to effectively prevent discoloration anddarkening of par-fried potato food, which includes French fries, slicedpotato, scalloped potatoes, au gratin potatoes, and the like. Thisinvention can also be applied in the production of potato-derivedproducts such as potato granules, potato flakes, potato proteinproducts, and potato starch.

In another aspect of the invention the composition includes calcium ionsin addition to the lactic acid. The addition of lactic acid has afurther advantage of preventing or at lest reducing the forming ofacrylamide, which is a toxic compound that is easily formed duringheating of potato products. Most preferred, the calcium ion is added inthe form of calcium lactate.

In the process of the invention, a composition is used to treat potatofood products. Such composition may apart from lactic acid furthercomprise another material or a mixture of materials fulfilling both therequirements of complexing chlorogenic acid and inhibiting oxidation, ormay be a combination of materials each fulfilling one of therequirements.

The composition used preferably comprises calcium lactate in a 0.1 to 3wt % aqueous solution, more preferably 0.4 to 0.8 wt %. The calciumlactate may advantageously be employed at a pH of about 3.5 or lower.Best results are obtained at pH lower than 3. This solution is used tocontact the potato food products for about 30 to 180 seconds. Accordingto this procedure the lactic acid, and if present the calcium lactate,fulfill both the requirement of complexing chlorogenic acid andinhibiting oxidation. The lactic acid prevents the chlorogenic acid tobe in the ionic form, whereas calcium ion complexes the chlorogenic acidand the lactate ion inhibits oxidation of the ferrous ion.

Alternatively, the process may include using a combination of 0.1 to 5wt % lactic acid, preferably 0.3 to 1.5 wt %, 0 to 3 wt % calciumlactate with about 0.1 to 1 wt % disodium acid pyrophosphate (SAPP). Itis current commercial practice for reducing after-cooking darkening inFrench fries to use 0.3 to 0.8 wt % SAPP solution. This inventionpermits a lower concentration of SAPP to be used or complete eliminationthereof in order to eliminate negative taste effects and to eliminatedetrimental effects to the environment. Lactic acid and calcium lactatebeing a natural and a non environmentally damaging product whileachieving an at least satisfactory or improved prevention ofafter-cooking darkening.

The invention is further illustrated by the following non-limitativeexamples.

Various calcium salts were tested with or without SAPP, focusing on thecolorization of potatoes. Severe precipitation occurred.

Materials

Potatoes, table potatoes (ex Nettorama)

Calcium lactate Pentahydrate food grade (ex Purac)

Calcium acetate (ex Acros; analytical grade)

Calcium chloride anhydrous (ex Acros; analytical grade)

Disodium acid pyrophosphate (ex Budenheim) PURAC 80 (ex Purac; lacticacid food grade)

Method

Washing and Slicing Potatoes.

The potatoes were sliced and kept in water until use.The potatoes were blanched for 3 minutes at approx. 70° C., Slices ofone potato were distributed over 12 different washing bags, one bag persolution and thereafter dipped for 2 minutes at 50° C. in 600 ml of atest solution.The excess of water was removed from the slices, and the slices werestored in sample cups without lid to allow contact with air. After 24hours the colorization was evaluated, and samples were ranked accordingto color from “bad” (black) color to “good” yellowish color by a threepanel expert panel and the pH of solutions were measured.The compositions are given in table I:

pH of solutions Ca Ca Ca before Entry SAPP¹⁾ lactate acetate chloride LAdipping  1 0.5 0.6 2 2.86  2 0.5 0.6 1 3.21  3* 0.5 0.6 0 4.09  4 0.20.6 1.2 3.11  5 0.2 0.6 0.6 3.44  6* 0.2 0.6 0 4.10  7 0.1 0.6 0.6 3.43 8 0.1 0.6 0.3 3.78  9* 0.1 0.6 0 4.31 10 0.5 0.2 0.2 1 2.77 11* 0.5 0.20.2 0 3.51 12 0.2 0.2 0.2 0.6 2.94 13* 0.2 0.2 0.2 0 3.68 14* 0 0.6 06.75 15* 0 0.2 0.2 0 7.11 16 0 0.6 1 3.18 17* 0 0.308 0 7.33 18* 0 0.2860 6.90 19 0 0.308 1 3.31 20* 0 0 6.60 21* 0.5 0 4.61 22* 0.2 0 4.76 230.1 0 4.84 ¹⁾all values are in wt % *according to prior art

In Table 2 the samples were judged on color and ranked from bad (black)to good (yellowish).

Entry Evaluation based on color Precipitation 18* 20* 15* 17* Allsamples suffer from severe 14* colorization, black outer 23* layers 21* 9* severe 11* Colorization of outer layers severe 22* less intensecompared to above  3* mentioned samples severe 7 16  19  Samples are toowhite 8  6* severe 10  Slight colorization around pit 13* severe 12  5Good color, slightly yellow 4 2 1

The entries indicated with an asterisk are compositions according to theprior art. As can be seen, the prior art compositions show strongafter-cooking darkening, with the exception of entries 6 and 13. Priorart entries 6 and 13, however, show severe precipitation of SAPP, forwhich these are undesired. The entries according to this invention (1,2, 4, 5, 7, 8, 10, 12, 16, and 19) showed reasonable to excellentreduction of darkening and no precipitation of SAPP. Best results wereobtained with compositions comprising lactic acid, calcium lactate andSAPP (entries 1, 2, 4, 5, and 12). A similar composition having muchlower calcium lactate content (entry 10) is slightly less advantageous).

1. A process for preventing or reducing after-cooking darkening inpar-fried potato food products, comprising forming treated potato foodproducts by contacting blanched potato food products with a compositioncomprising lactic acid.
 2. The process according to claim 1, wherein thelactic acid is present in 0.1 to 5 wt. %, preferably in 0.3-1.5 wt % ofthe composition.
 3. The process according to claim 1, wherein thecomposition includes calcium ions.
 4. The process according to claim 3,wherein the composition includes calcium lactate
 5. The processaccording to claim 1, wherein the composition includes disodium acidpyrophosphate (SAPP).
 6. The process according to claim 3, wherein thecomposition includes SAPP.
 7. The process according to claim 3, whereinthe calcium ions are up to 0.4 wt % of the composition.
 8. The processaccording to claim 5, wherein the amount of SAPP is in a concentrationof 0.1 to 1 wt %.
 9. The process according to claim 1, wherein the pH ofthe composition is smaller than 4.0, preferably smaller than 3.5.